1. Field of the Invention
The present invention relates to an exposure apparatus used in photolithography, and more particularly, to an exposure apparatus capable of forming exposed parts inside a photoresist layer which parts have a flared shape gradually broadening along the direction perpendicular to the surface of the photoresist layer.
2. Description of the Related Art
Photolithography techniques are used to form very fine patterns in a variety of applications, principally in the field of large-scale integration circuits (LSI). More particularly, in recent years, with progress in nano-technology, the use of photolithography has expanded into fields beyond electrical circuits or semiconductor elements, such as processing of display screens, nozzle plates for inkjet heads, and the like.
Photolithography requires an exposure apparatus in order to expose the photoresist. At present, there are exposure apparatuses of a type which performs exposure by placing a photomask and a substrate coated with the photoresist in contact with each other, a type which performs exposure by placing the photomask and the substrate coated with the photoresist in proximity to each other (maintaining a small gap between them), and a type which projects a pattern formed in the photomask onto the substrate coated with the photoresist, through a projection optical system, at the same size, or a magnified or reduced size.
In the contact type exposure system, there are other exposure apparatuses as described in Japanese Patent Application Publication Nos. 55-7799 and 2005-173129, in which a photoresist is applied on a side of a photomask, and the pattern of the photomask is transferred to the photoresist by projecting light to the other side of the photomask, which is not coated with the photoresist. In particular, in the method described in Japanese Patent Application Publication No. 2005-173129, it is possible to expose the photoresist in a tilting state and to form an oblique exposure pattern in the photoresist layer, by obliquely projecting light to the photomask.
In the exposure apparatuses, there are limitations on the resolution since light is used, and hence the degree of miniaturization that can be achieved in the pattern formed in the exposure region is also restricted as a result of this limited resolution. In order to improve the resolution limits, as disclosed in Japanese Patent Application Publication No. 57-153433, there is a method known as immersion exposure, in which the substrate coated with the photoresist to be exposed is immersed in liquid, such as water, and is then exposed with light in the liquid. According to this method, it is possible to improve the resolution limitations during exposure, and very fine patterns that are difficult to achieve with a normal exposure method can be easily formed.
However, depending on the application for which photolithography is used, there may be cases where it is wished to change the shape of the exposure pattern formed in the photoresist, in the depth direction of the photoresist layer. For example, when forming nozzle shapes for an inkjet apparatus by photolithography, it is required that the flare angle of the exposure pattern is changed along the direction perpendicular to the surface of the photoresist layer. An exposure pattern having a shape of this kind cannot be formed readily by using any of the exposure methods described in the above-described related art.